A practical power generation system utilizing electrostatic induction by an electret material has been disclosed in PLTs 1 to 3. “Electrostatic induction” is the phenomenon of an electric charge of a reverse polarity from an electrically charged object being attracted if the electrically charged object is made to approach a conductor. A power generation system utilizing the phenomenon of electrostatic induction utilizes this phenomenon in a structure provided with a “film holding an electric charge” (below, referred to as an “electrically charged film”) and a “counter electrode”. It makes the two move relative to each other to induce an electric charge and takes it out to generate power.
Taking the case of an electret material as an example, an electret is a dielectric material which has a charge and forms a quasi-permanent electrostatic field. In generation of power by this electret, as seen in FIG. 1. The electrostatic field formed by the electret 3 causes an induced charge at the counter electrode (electrode) 2. If changing the overlapping area of the electret and counter electrode (vibration etc.), it is possible to generate an AC current at an external electrical circuit 200. The generation of power by this electret utilizes a relatively simple structure and is based on electromagnetic induction, so can generate a high output in the low frequency region. It is therefore advantageous and is being focused on in recent years for so-called “energy harvesting”.
PLT 1 discloses a portable vibration power generator utilizing the low frequency vibration caused by motion of the human body as external energy by a horizontal vibration type electret device. PLT 2 discloses a power generation system utlizing electrostatic induction such as used for a mechanical type self-winding wristwatch which transmits the rotation of a rotor increased in speed through a gear mechanism to make the electret film and electrode rotate relatively. Further, PLT 3 discloses a power generation system utilizing electrostatic induction to periodically drive back and forth motion of an electret film and electrode wherein the rotor is supported through an elastic member and the rotor is made to vibrate sympathetically. The prior art of PLT 3 uses the elastic member to cause sympathetic vibration to increase the amplitude of rotation and improve the power generation efficiency. However, in these prior art, in each case, the technical idea of accurately controlling the gap between the electret film and electrode to try to raise the power generation efficiency is not shown in any way.
Further, PLT 4 discloses a mechanism of a clock in which backlash of a screw part of a bearing part at a balance staff or shaft of an escape wheel or other shaft is eliminated by insertion of a spring washer. However, in a conventional mechanical type clock, there is no need for accurate positioning of the shaft in the axial direction. Not only this, the technical idea of accurately controlling the gap between the electret film and electrode to try to raise the power generation efficiency is not shown at all.